Inferring typesetting board counts in early Korean metal-type printing via character-structure similarity

While movable metal-type printing in Goryeo and Joseon dynasties enabled efficient book production, certain aspects of the process remain insufficiently understood. We propose a method to estimate the number of typesetting boards used in historical metal-type printing, offering valuable insights into the scale of metal-type production at the time. Because the book title printed repeatedly on each sheet exhibits distinctive characteristics of individual typesetting boards, typesetting board counts can be inferred by clustering similar instances of the book title, implying that titles within the same cluster were printed using an identical board. To quantify the visual similarity among printed characters, we propose Character-Structure Similarity Measure (CSSM) providing robustness against variations in stroke thickness and ink spread. Experiments on seven 14th-16th century Korean metal-type books show CSSM outperforming conventional metrics in accuracy and clustering performance. This methodology contributes to historical printing studies, supporting bibliographic research, cultural heritage preservation, and digital humanities.